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Leaf respiration in two tropical rainforests: constraints on physiology by phosphorus, nitrogen and temperature
Author(s) -
Meir P.,
Grace J.,
Miranda A. C.
Publication year - 2001
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1046/j.1365-2435.2001.00534.x
Subject(s) - phosphorus , rainforest , respiration , biology , nitrogen , canopy , nutrient , zoology , botany , nitrogen cycle , carbon cycle , ecology , ecosystem , chemistry , organic chemistry
Summary1 Leaf respiration is a major component of the terrestrial carbon cycle, but is poorly quantified for tropical forests. We measured dark respiration, R , and nutrient concentration (nitrogen, N and phosphorus, P ) of leaves within two forest canopies: in Reserva Jarú, south‐west Brazil; and Mbalmayo Reserve, central Cameroon. The data, expressed on a leaf area basis ( R a , N a , P a ) and a leaf mass basis ( R m , N m , P m ), were used to quantify the temperature sensitivity of R and to test the hypothesis that leaf metabolism is more strongly constrained by phosphorus than by nitrogen in these lowland rainforests. 2 Leaf respiration rate ( R a , at 25 °C) at Jarú was nearly half that at Mbalmayo (the range in R a from near the ground to the upper canopy was 0·11–0·78 µmol m −2 s −1 at Jarú versus 0·22–1·19 µmol m −2 s −1 at Mbalmayo), and the mean Q 10 for respiration at each site was 2·3 ± 0·9 (1 SD) and 2·0 ± 0·5 (1 SD), respectively. There were significant differences ( P < 0·01) between sites in leaf phosphorus concentration, but not in leaf nitrogen concentration: P m was very low at Jarú (0·2–0·7 mg g −1 ) but higher at Mbalmayo (0·5–2·4 mg g −1 ), whilst N m was similar at both forests (10–45 mg g −1 ). 3 R m was not significantly associated with canopy position or specific leaf area (SLA, m 2 g −1 ) in either forest, but a significant relationship between SLA and N m was found for both sites ( P < 0·05), consistent with existing data. At Jarú, R m was strongly related to P m ( P < 0·001) and less strongly related to N m ( P < 0·05), but at Mbalmayo, R m was not significantly related to either P m or N m . 4 R a was linearly related to N a and P a at both sites ( P < 0·01), principally because of changes in leaf mass per area (LMA, g m −2 ) associated with canopy position. At Mbalmayo, LMA explained 70% of the variation in R a , but only 20% at Jarú. For Jarú, the strongest relationship with R a was obtained by combining LMA with P m in a multiple regression ( r 2 = 0·53); further inclusion of N m did not improve the regression. At Mbalmayo neither N m or P m improved the regression of R a on LMA. 5 These results indicate a strong influence of LMA on the relative rates of R a within the vertical gradient of each canopy. They also suggest that at Jarú P m constrains respiration more strongly than N m , and further, that the very low P m at Jarú may explain the lower absolute values of respiration there relative to Mbalmayo, where P m was higher. The leaves at both sites are typical of lowland tropical rainforests in not having particularly low N m , and consistent with this, N m was a weaker predictor of respiration than P m or LMA.